This invention relates to a method of preparing rapid curing pressure sensitive adhesives comprising an acrylic interpolymer and a chelated metal alkoxide. These adhesives exhibit fast crosslinking cure rates while retaining good tack, cohesive strength and other adhesive properties making them useful in a number of applications, particularly those requiring rapid coating line speeds.
Pressure sensitive adhesives function to provide instantaneous adhesion when applied under light pressure. They are characterized by having a builtin capacity to secure this adhesion to a surface without activation, such as by treatment with solvents or heat, and also desirably having sufficient internal strength so that the adhesive material will not rupture before the bond between the adhesive material and the surface ruptures The capacity to obtain instantaneous adhesion is usually expressed as the amount of "track" or "tackiness." Ordinarily it is desirable to obtain as much tack as possible without losing a significant amount of internal strength (cohesion). The latter balance of adhesive and cohesive properties has been difficult to obtain in adhesive polymers since modifications to increase the cohesive strength generally result in a decrease in adhesive tack.
Pressure sensitive adhesive systems based on acrylic interpolymers and typically applied to substrates from solutions have been developed over more than thirty years. Such adhesives generally have been found to have suitable tack and cohesive properties as well as possessing other adhesive properties required for specific applications. U.S. Pat. No. B1 3,769,254 issued Feb. 26, 1985 discloses pressure sensitive adhesives formed by reacting a metal alkoxide with an interpolymer comprised of an alkyl acrylate, an acrylic monomer containing a reactive hydrogen atom and a copolymerizable ethylenically unsaturated monomer. U.S. Pat. No. 4,185,051 issued Jan. 22, 1980 discloses acrylic interpolymers containing hydroxyl or carboxyl groups reacted with poly (metaloxane) as pressure sensitive adhesive with improved color, cohesive strength and tack. U.S. Pat. No. 3,740,366 issued June 19, 1973 shows adhesive prepared polymers containing a carboxylic acid group and crosslinked with a polyvalent metal. U.S. Pat. No. 4,292,231 issued Sept. 29, 1981 discloses pressure sensitive adhesives having improved cohesive strength formed by reacting acrylic interpolymers containing a vinyl monomer having both a carboxyl and carbonate functional group with a metal alkoxide. U.S. Pat. No. 3,886,126 issued May 27, 1975 shows pressure sensitive resin solutions containing chelate esters of orthotitanic acid and interpolymers having an hydroxyl, carboxyl or enolizable keto group. U.S. Pat. No. 3,532,708 issued Oct. 6, 1970 discloses rapid room temperature curable pressure sensitive adhesive resins comprising an interpolymer which includes an hydroxyl bearing acrylate, methacrylate, maleate or fumarate monomer and a metal alkoxide. U.S. Pat. No. 4,005,247 issued Jan. 27, 1977 discloses pressure sensitive adhesives with improved cohesive strength and good tack formed by reacting an acrylic interpolymer of an alkyl acrylate and ethylenically unsaturated acid anhydride with a metal alkoxide.
The above noted disclosures show various pressure sensitive adhesives which provide different property characteristics, especially cohesive strength and tack, making them useful in a number of applications. However, there are other applications which require improved conditions such as an accelerated crosslink curing rate to provide faster processing operations and avoid problems such as cold flow or adhesive edge ooze.